Honda Car Forum

A customer brought in a 94 Civic with an AC concern. The system is tight
and charged but the compressor won't engage. I was able to check the
system back to the AC relay and found that whatever grounds the
relay...doesn't. I don't have a wiring diagram, Is there anything
between the coil ground pin of the relay and the switch on the
instrument panel? I suspect the switch. If I had the pinout for the
switch I can troubleshoot from there. Can anyone provide this
information? IIRC there are 5 pins on the switch. I've got 1 pin with
switched power and 1 ground for sure. I imagine 1 is for the
illumination of the switch. That leaves 2 unknown terminals.Any input
would be appreciated.
Thanks, Tom

remove wrote:

> relay...doesn't. I don't have a wiring diagram, Is there anything
> between the coil ground pin of the relay and the switch on the
> instrument panel?

Yes. The relay coil ground pin is connected to the ECU. When the ECU
gets a request for A/C, it will delay turning on the relay while it
enriches the air/fuel mixture a bit. The A/C request comes to the ECU
through the A/C pressure switch, the A/C thermostat at the evaporator,
the A/C main switch and the ventilation fan switch.

> Isuspect the switch. If I had the pinout for the
> switch I can troubleshoot from there. Can anyone provide this
> information? IIRC there are 5 pins on the switch.

That's a lot of pins, don't recall it having that many. Are you sure
this is an OEM Honda A/C? I once had a Civic where the dealer had
installed an after-market A/C.

> I've got 1 pin with
> switched power and 1 ground for sure. I imagine 1 is for the
> illumination of the switch. That leaves 2 unknown terminals.Any input
> would be appreciated.
> Thanks, Tom

You can find the wiring diagram at
http://www.honda.co.uk/owner/civicmanual/pdf/22-6.pdf. This wiring
diagram is for the European Civic, but it is identical to the US version
with three minor exceptions:

1. Ground for the condenser fan goes to ground location G751 (EU: 701)

2. Thermal protector for the compressor is shown as a separate item in
the above referenced schematic. In the US schematic it is not shown, but
it is still installed in the car (internal to the compressor)

3. The A/C on indicator in the EU schematic is shown as a simple light
bulb. In the US variety it is shown as an LED connected through a
dimming circuit.

I have compared the above referenced .pdf with the wiring diagram in the
Helm manual for my '94 Civic, and find only the above mentioned
discrepancies. Wire colors, fuse numbers and ratings etc. match.

A couple of trouble shooting tips: If the A/C-on indicator does not turn
on, the problem is in the A/C main switch, or, more likely, in the
ventilation fan switch.

If the condenser fan comes on but the compressor does not, the most
likely problem is the A/C pressure switch. It could be a faulty pressure
switch, or improper pressure in the system. I do not know if this is a
high pressure lockout or a low pressure lockout. I have seen both on
various cars.

Randolph wrote:
> remove wrote:
>
>
>>relay...doesn't. I don't have a wiring diagram, Is there anything
>>between the coil ground pin of the relay and the switch on the
>>instrument panel?
>
>
> Yes. The relay coil ground pin is connected to the ECU. When the ECU
> gets a request for A/C, it will delay turning on the relay while it
> enriches the air/fuel mixture a bit. The A/C request comes to the ECU
> through the A/C pressure switch, the A/C thermostat at the evaporator,
> the A/C main switch and the ventilation fan switch.
>
>
>>Isuspect the switch. If I had the pinout for the
>>switch I can troubleshoot from there. Can anyone provide this
>>information? IIRC there are 5 pins on the switch.
>
>
> That's a lot of pins, don't recall it having that many. Are you sure
> this is an OEM Honda A/C? I once had a Civic where the dealer had
> installed an after-market A/C.
>
>
>>I've got 1 pin with
>>switched power and 1 ground for sure. I imagine 1 is for the
>>illumination of the switch. That leaves 2 unknown terminals.Any input
>>would be appreciated.
>> Thanks, Tom
>
>
> You can find the wiring diagram at
> http://www.honda.co.uk/owner/civicmanual/pdf/22-6.pdf. This wiring
> diagram is for the European Civic, but it is identical to the US version
> with three minor exceptions:
>
> 1. Ground for the condenser fan goes to ground location G751 (EU: 701)
>
> 2. Thermal protector for the compressor is shown as a separate item in
> the above referenced schematic. In the US schematic it is not shown, but
> it is still installed in the car (internal to the compressor)
>
> 3. The A/C on indicator in the EU schematic is shown as a simple light
> bulb. In the US variety it is shown as an LED connected through a
> dimming circuit.
>
> I have compared the above referenced .pdf with the wiring diagram in the
> Helm manual for my '94 Civic, and find only the above mentioned
> discrepancies. Wire colors, fuse numbers and ratings etc. match.
>
> A couple of trouble shooting tips: If the A/C-on indicator does not turn
> on, the problem is in the A/C main switch, or, more likely, in the
> ventilation fan switch.
>
> If the condenser fan comes on but the compressor does not, the most
> likely problem is the A/C pressure switch. It could be a faulty pressure
> switch, or improper pressure in the system. I do not know if this is a
> high pressure lockout or a low pressure lockout. I have seen both on
> various cars.

Hey, Thank you very much. That is exactly what I needed. The AC switch
was indeed defective.